Supine hypertension, blood pressure variability and circadian rhythm in autonomic failure: the role of ambulatory intra-arterial monitoring.

Blood pressure variation over 24 h was studied in twelve subjects with suspected or established autonomic failure using ambulatory intra-arterial monitoring. Three subjects who had been previously diagnosed as having orthostatic hypotension due to autonomic failure were found to have normal circulatory reflexes. A generally consistent circadian variation of blood pressure was seen in the other nine subjects, pressure rising gradually from its lowest point early in the morning to a peak during the early part of the night; this pattern was also found during bed rest in four subjects. Supine hypertension (an hourly mean blood pressure of greater than 170/90 mmHg) not suspected from sphygmomanometric readings was observed in four subjects, generally during the night. Heart rate variability was reduced in six subjects while short-term blood pressure variability was markedly increased.